WO2021005469A1

WO2021005469A1 - Load cell device

Info

Publication number: WO2021005469A1
Application number: PCT/IB2020/056257
Authority: WO
Inventors: Gilberto ROMBOLI
Original assignee: Nanolever S.R.L.
Priority date: 2019-07-09
Filing date: 2020-07-02
Publication date: 2021-01-14
Also published as: IT201900011244A1

Abstract

A load cell device (100), which may be used e.g. to implement weighing scales embedded in cooking surfaces, comprises: a plate-like body (140) having opposed first and second surfaces, the plate-like body (140) deformable as a result of a pressure force (R) applied onto the first surface (170), - an elongated body (120) having a first end (120a) fixed (180) at the periphery of the plate-like body (140) and a second end (120b) in a force-transmission relationship (160) with the second surface of the plat- like body (140). As a result of deformation of the plate-like body (140), the elongated body (120) is subject to bending, and a strain gauge detector (180) coupled with the first end (120a) of the elongated body (120) is configured (200, 200A) to provide a sensing signal indicative of the amount of bending of the elongated body (120). The sensing signal is a function of the pressure force applied onto the first surface (170) of the plate-like body (140).

Description

"Load cell device"

k k k k

Technical Field

The present description relates to load cell devices.

One or more embodiments may be applied in weighing devices such as, for example, such devices which are adapted to accommodate, below a support for the goods to be weighed, equipment adapted to process, transform or analyse the products during weighing.

One or more embodiments may find an advantageous, albeit non-limiting, application in the field of cooking devices .

Technological Background

A load cell is a transducer adapted to measure a force applied onto a body. A current application of load cells regards electronic weighing systems and the measurement of mechanical compressive and tensile stresses .

For example, a load cell may comprise a measuring body, for example made of steel or aluminium, on which a force is applied which determines a deformation thereof. According to the structure of the body, said deformation may involve compression, traction, bending or a combination thereof.

A conventional load cell may employ one or more strain gauges which, being applied at certain locations of the measuring body, are adapted to detect the deformation thereof through the variation of electrical resistance induced by such deformation into their electrical circuit. The obtained electrical signal may be amplified and processed in order to determine the force applied onto the body of the load cell.

For example, there are known load cells comprising S-shaped measuring bodies, which are subject to traction or compression along an axis passing through the center of the body.

There are also known so-called "off-center" load cells, which comprise a parallelepiped-shaped body, wherein a butterfly-shaped through-opening is present which enables the body, mounted in a cantilever manner on a support, to bend while following the movement of a parallelogram.

Solutions of this type are described e.g. in EP 3 343 187 A1 or in the International Application

PCT/IB2019/05695, as yet unpublished on the filing date of the present application.

As compared with the load cells operating through traction or compression, the off-center cells offer the advantage of enabling the accommodation on the cell of a rectangular "weighing plane", having dimensions not higher than twice the maximum length of the cell itself (which may be as long as about 170 mm), on which plane the product to be weighed may be arranged, without requiring any alignment between the applied loads and the deformation axis of the measuring body.

With reference to existing patents, documents such as WO 95/35483, US 4 476 946 A, US 6 541 742 B2 or WO 2015/181 763 A2 exemplify the possibility of applying load cells or like devices to cooking devices.

Even neglecting various disadvantages exhibited by such prior art documents, it may be observed that currently no load cell is available which enables mounting weighing plates having a size of several tens of centimeters.

For example, US 5 183 126 A describes a weighing device comprising an element substantially similar to a supported beam, which is subject to a bending load, wherein the loads applied are detected by a strain gauge which is mounted in a central position. US 2015/292965 A1 describes a load cell having a bending element, which implements a so-called Roberval mechanism consisting of a pair of a top and a bottom parallel beams, comprising thin sections with associated strain gauges.

EP 1 347 273 A1 describes a weighing cell which is substantially similar, having resistive strain gauges which are arranged symmetrically with reference to the lengthwise axis of the bending element.

Such known solutions are not adapted to implement weighing scales which are destined e.g. to be mounted into cooking surfaces: in such applications, the vessel arranged on the cooking surface (which may be considered as a part of the weighing system) may actually have significantly varying sizes.

Object and Summary

One or more embodiments aim at providing improved solutions which are adapted to be used with satisfying performances in various possible application scenarios, such as e.g. the contexts previously discussed in the introduction of the present specification.

According to one or more embodiments, such object may be achieved thanks to a load cell device having the features specifically set forth in the claims that follow.

The claims are an integral part of the technical teachings provided herein with reference to the embodiments .

One or more embodiments help overcoming possible limitations regarding the deflection deriving from applying onto the cell a load corresponding to products to be weighed.

In traditional load cells, the deflection deriving from the load applied may reach a maximum value of about 0.2 mm; beyond that, the cell material may be exhibit yielding .

One or more embodiments enable achieving deflection values around 1.5 mm. As a consequence, the (micro ) strain gauges of the cells may have a much larger deformation range (even 100 times as large as the traditional cells) : this brings about a remarkable rise in the cell sensitivity, enabling for example increasing the divisions of the measuring range, with a consequent higher accuracy of the measuring result.

Brief Description of the Figures

One or more embodiments will now be described, by way of non-limiting example only, with reference to the annexed Figures, wherein:

- Figure 1 is an elevation view, partially in cross- section, of a load cell according to embodiments,

- Figure 2 is an exploded perspective view of a measuring device adapted to include embodiments.

Detailed Description of Embodiments

In the following description, various specific details are given to provide a thorough understanding of exemplary embodiments. The embodiments may be implemented without one or several specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials or operations are not shown or described in detail in order to avoid obscuring certain aspects of embodiments.

Reference throughout this specification to "an embodiment" or "one embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the possible appearances of the phrases "in an embodiment" or "in one embodiment" in various places throughout this specification are not necessarily all referring to one specific embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The headings provided herein are given for convenience only, and therefore do not interpret the extent of protection or scope of the embodiments.

In the figures, reference 100 denotes a load cell, shown in a 3D reference system. In such a system a first lengthwise direction X and a second transversal direction Y, which are mutually perpendicular, define a horizontal plane, and a third vertical direction Z indicates a direction which is perpendicular to the horizontal plane, along which the force of gravity is acting .

As exemplified herein, load cell 100 includes a frame-shaped base 110, which supports a deformable body 140, e.g. a plate-like body which is generally planar.

Albeit illustrated, for simplicity, as having a quadrilateral (e.g. rectangular) shape, both the deformable body 140 and the base 110 may have a different shape, e.g. circular or polygonal.

As exemplified herein, load cell 100 comprises an elongated measuring body 120, which is arranged below the deformable body 140 and extends in a cantilever fashion from the periphery towards the central region of deformable body 140 (for example in a lengthwise direction X) , having the general shape of a diving-board.

As exemplified herein body 120, which is equally deformable, is in a (pressure) force-transmission relationship with body 140.

This may take place e.g. via a pin 160 which is placed at the second (distal) end of body 120, e.g. in the central region of deformable body 140.

Ad exemplified herein, body 120 extends in the lengthwise direction X for about half the total length of base 110, so that it may have a length selectable within a rather large range of values.

As exemplified herein, in the transversal direction Y, body 120 may have a dimension (width) of a few tens of millimeters.

In one or more embodiments, the thickness of body

120 in direction Z may be chosen so that the deflection which may be detected at the distal end of the beam represented by body 120, in the position of pin 160, in the presence of the predetermined maximum weigh load (full scale of the cell) is not as high as to induce a yield in the e.g. metallic material of body 120.

In one or more embodiments, the body 140 which defines the weighing plane may be implemented (e.g. as regards dimensions such as thickness) in such a way that, in the presence of the predetermined maximum weigh load being applied in a central position (e.g. at the crossing of the diagonals of a quadrilateral shape) , the vertical displacement of deformable body 140 along axis Z in the region where the weight is applied is not higher than the maximum deflection predetermined for the deformable body 120.

In one or more embodiments, the first (proximal) end 120a of deformable body 120 may be firmly fixed at the edge of body 140 (for example at one of the opposed surfaces of body 140, such as the lower surface) .

For example, as exemplified in Figure 1, this may be via a socket 130 fixed to the body 140 and/or, optionally, to base or frame 110, while the second (distal) end 120b carries pin 160 (the maximum diameter whereof being e.g. 2 mm), which is firmly held contacting the (lower) surface of deformable body 140, as a scanning device .

Using the terminology currently employed in science of constructions, body 120 may be seen as a cantilever beam, which is firmly fixed at 120a and which is (only) subject to a bending moment, optionally with a given bias deriving from pin 160 pressing against the surface of body 140, due to the bending of body 140, resting on frame 110, caused by the mass weight thereof.

In the presently exemplified embodiment, body 140

(e.g. with body 120 mounted thereon via socket 130) may be freely supported by the edges of frame 110, while being optionally kept away from frame 110 by a distance (e.g. by 10 mm) through the interposition of a gasket 150, which may be (e.g. plastically) resilient, e.g. by being few millimeters wide, which is applied around the periphery of deformable body 140.

As shown by the dotted line in Figure 2, on deformable body 140 it is possible to discern a load region 170, which is destined to receive a load (weight) acting in the vertical direction Z. The load region 170 is adapted e.g. to accommodate a vessel R, such as a tray containing a product to be weighed.

In the presently exemplified embodiment, a calibration of cell 100 may be carried out in region 170, while taking into account that the displacement of the load on the surface of body 140 may involve a variation of the deformation function of body 140 itself.

In one or more embodiments it is possible to envisage, in the body 140 which may be formed e.g. of metal, a sculptured portion, e.g. a recessed portion (shown in dotted lines and denoted as V in Figure 1), or a simple serigraphy wherein said vessel R may be inserted, so that the latter can be located accurately with respect to region 170.

In addition or as an alternative, in one or more embodiments, e.g. when the body 140 is made of glass or glass-ceramic, it is possible to provide a similar centering system of vessel R with respect to region 170 via permanent magnets or via markers M, which help visually center the tray.

One or more embodiments are based on the acknowledgement that a force applied onto region 170 (in a vertical direction along axis Z, from top to bottom in the view of the annexed Figures) e.g. by a vessel R which contains a material to be weighed, causes (an elastic) bending of deformable body 140, which moves towards deformable body 120 with which it is in a force- transmission relationship, e.g. via pin 160.

Because of the mechanical connection between the deformable body 140 and the body 120 (which is implemented by the pin 160 located at the second end 120b of body 120), body 120 which acts as a measuring body deforms by bending in the direction of axis Z, without rotating with respect to plane XY.

Consequently, the deformable body 120 is (only) subject to a bending moment, with a maximum deformation detectable at the first end 120a of body 120, i.e. in the area of the fixed connection formed in this case by the socket 130.

Such deformation can be detected by one or more strain gauge detectors 180, which are applied onto body 120 in this area of maximum deformation.

The strain gauges may be for example electrical (e.g. resistive) strain gauges.

In one or more embodiments there may be provided a plurality, e.g. two, of strain gauges 180, applied onto body 120 above and under body 120.

In one or more embodiments, the one or more strain gauges 180 are glued onto body 120.

In one or more embodiments, the signal (s) indicative of the electrical voltage (or the electrical voltage variation) provided by strain gauge (s) 180 may be forwarded to an electronic circuit 200 (of a kind known in itself) in order to be processed and converted into the values of the weight applied onto plane 140.

In one or more embodiments, the electronic circuit 200 may be configured in such a way as to take into account a calibration factor regarding the measurement position (region 170) on deformable body 140, and in order to determine a weight value of the material arranged on plane 140.

For example, such calibration values (and a corresponding regulation of the gain factor applied by circuit 200 to the strain gauge signals) may be determined by applying a known weight in the measurement region 170.

Optionally, the electronic circuit 200 may be configured (again, in a way known in itself) so that it may take into account the tare weight of vessel R.

In any case, the thus determined weight value may be represented visually, e.g. on a display 200A, e.g. a "seven-segment" display which is associated to and driven by electronic circuit 200.

In one or more embodiments it is possible to associate to plane 140 an RFID tag reader (which is e.g. embedded into plane 140 and/or into circuit 200) which is adapted to read RFID tags provided on the vessels which contain the material to be weighed. Such tags may indicate the weight of the vessel, which is read by the electronics of the scale and which may then be used to calibrate the plane each time it accommodates a tagged vessel .

The presently exemplified load cell 100 may be employed directly as a weighing scale, offering the possibility of accommodating, in a hollow space defined by frame 110 below the deformable body 140, various devices H which may process (e.g. analyse, heat or cook) the material contained within vessel R, while at the same time weighing the same for as long as desired, until the end of the process.

A load cell 100 as exemplified herein may include a weighing plane formed by a body 140 of elastically deformable material, the contour whereof may rest (if desired with a liquid-tight sealing, see e.g. gasket 150) on a frame 110. There is provided a bending beam (body 120) an end 120a whereof is firmly fixed at an edge of the weighing plane 140, while the other end 120b whereof is put into a force-transmission relationship (e.g. through a pin 160 fixed at the end of the beam, or optionally in direct contact) with the (lower) surface of the weighing plane 140.

Because the (elastically deformable) weighing plane 140 rests along its contour on a frame 110, the load (weight) arranged on plane 140 e.g. in a central region 170 causes the beam formed by body 120 to bend, e.g. with an exclusive bending moment, a maximum deflection being reachable at second end 120b at the predetermined maximum load, and being determined in such a way as to avoid yield in the (e.g. metallic) material of which it is made.

The deformation of beam (body 120) may be translated into a sensing electrical (e.g. voltage) signal by one or more (e.g. resistive) strain gauges 180 which are applied, e.g. glued, at first end 120a, where the bending moment associated to the load makes deformations higher (of a maximum value) .

Such a solution simplifies the calibration of the load cell for different loads, while remaining within the limits of the structural features of the weighing plane .

For example, in one or more embodiments, the calibration of cell 100 may be carried out with reference to region 170 of the weighing plane 140 where the mass to be weighed is going to be arranged, so that a good measurement repeatability is achieved.

As stated in the foregoing, in one or more embodiments, along the edges of the weighing plane 140 resting on frame 110 it is possible to apply a plastic gasket 150, which is adapted to offer a proper protection against the penetration of water and dust below weighing plane 140.

This helps preserving the full working efficiency of the load cell in the course of time.

In one or more embodiments, the materials forming the weighing plane 140 and the bending beam 120 may exhibit an elastic behaviour within the range of the loads to be measured.

For example, in one or more embodiments, the weighing plane (body 140) and the bending beam (body

120) may be made of metal and optionally of glass or glass-ceramic, or of other materials, depending on the application and usage requirements for the load cell.

A load cell device (e.g. 100) as exemplified herein may include:

- a plate-like body (e.g. 140) having opposed first and second surfaces (e.g. a top and a bottom surface, in a possible mounting condition) , the plate-like body being deformable as a result of a pressure force (for example, the weight of a vessel R and of the content thereof) applied onto the first surface (e.g. at 170),

- a (measuring) elongated body (e.g. 120) having a first end (e.g. 120a) fixed (e.g. via 180) at the periphery of the plate-like body, and a second end (e.g. 120b) in a force-transmission relationship with the second surface of the plate-like body, wherein the elongated body is subject to bending as a result of deformation of the plate-like body, and

a strain gauge detector (e.g. one or more resistive strain gauges 180) coupled with the first end of the elongated body, the strain gauge detector being configured (e.g. 200, 200A) to provide a sensing signal indicative of the amount of bending of the elongated body, wherein said sensing signal is a function of the pressure force applied onto the first surface of the plate-like body.

A load cell device as exemplified herein may comprise a force-transmission formation, preferably a pin member (e.g. 160), providing said force-transmission relationship between the second end (120b) of the elongated body (120) and the second surface of the plate like body (140) .

In one or more embodiments, said force-transmission formation may include a deformed appendix or portion of the elongated body 120 and/or of the plate-like body

140. The use of an optionally sharp pin member 160 mounted on the elongated body (or optionally on the plate-like body 140) may be advantageous because it helps to achieve a practically point-shaped force-transmission relationship, which favors measurement accuracy.

In a load cell device as exemplified herein, the elongated body may have its first end coupled to the periphery of the plate-like body, to be carried thereby.

In a load cell device as exemplified herein, the first surface of the plate-like body may comprise a pressure force application region (e.g. 170), wherein said pressure force application region optionally comprises a central region of the first surface of the plate-like body.

In a load cell device as exemplified herein, the second end of the elongated body may be arranged in a force-transmission relationship with the second surface of the plate-like body at a location of said second surface of the plate-like body opposed said pressure force application region (e.g. 170) at the first surface of the plate-like body.

In a load cell device as exemplified herein, said pressure force application region may have centering formations (for example a V-shaped sculpturing, or magnetic centering elements, or visual markers M) associated therewith.

In a load cell device as exemplified herein, the plate-like body may be supported peripherally by a frame member ( e . g . 110) .

In a load cell device as exemplified herein, said frame member may be configured to provide, at the second surface of the plate-like body, a mounting space for processing equipment (for example equipment for analysis, heating or cooking H) of material arranged at the first surface of the plate-like body.

A load cell device as exemplified herein may comprise a gasket member (e.g. 150) between the periphery of the plate-like body and said frame member.

In a load cell device as exemplified herein, with the plate-like body configured to have a maximum amount of pressure force applied onto the first surface, the elongated body may be shaped and dimensioned to remain below the yield point in the presence of said maximum amount of pressure force applied onto the first surface of the plate-like body.

In other words, the pressure force R applied onto the first surface 170 has a predetermined maximum value, and the elongated body 120 has such a thickness that, when said pressure force R having said predetermined maximum value is applied onto the first surface 170, the material of the elongated body 120 stays below the yield point .

A load cell device as exemplified herein may comprise an RFID tag reader, configured to read RFID tags indicative of the weight of vessels arranged on said plate-like body 140.

A load cell device as exemplified herein helps achieving the previously outlined advantages thanks to the fact that the (single) elongated body 120 extends in a cantilever fashion from the periphery towards the central region of the plate-like body, with a strain gauge detector being coupled with the first end of the elongated body.

Without prejudice to the underlying principles, the implementation details and the embodiments may vary, even appreciably, with respect to what has been described herein by way of non-limiting example only, without departing from the extent of protection.

The extent of protection is determined by the annexed claims.

Claims

1. A load cell device (100), comprising:

- a plate-like body (140) having opposed first and second surfaces, the plate-like body (140) deformable as a result of a pressure force (R) applied onto the first surface ( 170 ) ,

- an elongated body (120) having a first end (120a) fixed (180) at the periphery of the plate-like body (140) and a second end (120b) in a force-transmission relationship (160) with the second surface of the plate like body (140), wherein the elongated body (120) is subject to bending as a result of deformation of the plate-like body (140), and

- a strain gauge detector (180) coupled with the first end (120a) of the elongated body (120), the strain gauge detector (180) configured (200, 200A) to provide a sensing signal indicative of the amount of bending of the elongated body (120), wherein said sensing signal is a function of the pressure force applied onto the first surface (170) of the plate-like body (140) .

2 . The load cell device (100) of claim 1, comprising a pin member (160)— providing said force-transmission relationship between the second end (120b) of the elongated body (120) and the second surface of the plate- like body (140) .

3 . The load cell device (100) of claim 1 or claim 2, wherein the elongated body (120) has its first end (120a) fixed (130) to the periphery of the plate-like body (140) to be carried thereby.

4. The load cell device (100) of any of the previous claims, wherein the first surface of the plate-like body (140) comprises a pressure force application region, wherein said pressure force application region preferably comprising a central region of the first surface (170) of the plate-like body (140) .

5 . The load cell device (100) of claim 4, wherein the second end (120b) of the elongated body (120) is arranged in a force-transmission relationship with the second surface of the plate-like body (140) at a location of said second surface of the plate-like body (140) opposed said pressure force application region at the first surface (170) of the plate-like body (140) .

6. The load cell device (100) of claim 4 or claim 5, wherein said pressure force application region has centering formations (V, M) associated therewith.

7 . The load cell device (100) of claim 6, wherein said centering formations (V, M) comprise:

- a sculptured portion (V) ,

- printed material,

- permanent magnetic material,

- markers (M) for visual centering,

at said pressure force application region of the plate-like body (140) .

8. The load cell device (100) of any of the previous claims, wherein the plate-like body (140) is supported peripherally by a frame member (110) .

9 . The load cell device (100) of claim 8, wherein said frame member (110) is configured to provide at the second surface of the plate-like body (140) a hollow space .

10 . The load cell device (100) of claim 8 or claim 9, comprising a gasket member (150) between the periphery of the plate-like body (140) and said frame member (110) .

11 . The load cell device (100) of any of the previous claims, wherein:

said pressure force (R) applied onto the first surface (170) has a predetermined maximum value,

said elongated body (120) has such a thickness that, when said pressure force (R) applied onto the first surface (170) has said predetermined maximum value, the material of the elongated body (120) stays below the yield point.

12 . The load cell device (100) of any of the previous claims, comprising an RFID tag reader (200) configured to read RFID tags indicative of the weight of vessels arranged on said plate-like body (140) .

13 . The load cell device (100) of any of the previous claims, wherein said elongated body (120) extends in a cantilever manner from the periphery towards the central region of the plate-like body (140) .